1. Field of the Invention
The present invention relates to a magnetic random access memory (MRAM) in which a magneto-resistive element is used as a memory cell.
2. Description of the Related Art
Magnetic random access memories have been noted as next-generation memory devices, and researches and developments has been carried out to put these memories to practical use. However, there remain many problems to be solved, such as current reduction, enhancement of a resistance to erroneous writing, and thermal disturbance countermeasures.
To solve these problems, in a conventional magnetic random access memory, several proposals have been made from aspects of a shape of a magneto-resistive element, and a writing system.
For example, as to the shape of the magneto-resistive element, shapes have been proposed such as a cross shape, a bean shape, and a trapezoidal shape. As to the writing system, systems have been proposed such as toggle and spin-injection (see e.g., U.S. Pat. Nos. 6,545,906, 6,256,223).
However, as to the shape of the magneto-resistive element, certain effects are obtained in the current reduction, but it is difficult to obtain a sufficient resistance to erroneous writing only by the shape. When the shape is complicated, working becomes difficult. When a conventional semiconductor element forming technique is used, the technique is disadvantageous for miniaturization of a memory cell.
Moreover, in the toggle system among the writing systems, there is a problem that it is difficult to reduce a current although certain effects are obtained with respect to the resistance to erroneous writing. Furthermore, in the spin-injection system, since it is difficult to reduce a spin-injection current (write current), it is impossible to sufficiently handle problems such as reduction of a cell size, thermal disturbance countermeasure, and device destruction.